#include <iostream>
    #include <fstream>
    using namespace std;
    ifstream fin("fractii.in");
    ofstream fout("fractii.out");
    int main()
    {
        int N;
        fin>>N;
        if(N%2==0)
        fout<<N+(n-1)*(N/2-1)+(N/2)*(N/2);
        else
        fout<<N+((N-1)/2)*((N+1)/2)+(((N+1)/2)-1)*(N-1);
        return 0;
    }